When taking a meter reading for billing of electricity or gas charges, a bill collector who reads the meter may at the same time enter the data into a portable printer and issue a receipt on the spot. In that case, the bill collector saves the entered data and the issued receipt data into the portable printer. The saved data are retrieved later using a personal computer or the like and processed. A portable printer having such a function is often used outdoors by home-delivery service personnel, sales personnel, etc. This type of printer is equipped with a paper exit port through which printed paper is ejected, for example, in order to issue a receipt or the like. The paper exit port is usually not covered. Consequently, when the person carrying the printer is caught in rain or passes through a dusty area, rain drops or dust particles may enter the interior of the machine through the paper exit port, adversely affecting the internal electronic precision parts, causing the moving parts to malfunction, or allowing the paper to get wet, resulting in a printing failure.
Further, since this type of portable printer is operated by a battery, the power switch has to be turned on and off constantly. However, as is often the case, the operator may forget to turn off the power switch when he or she is busy.
Patent document 1 discloses a portable electronic apparatus which aims to prevent printed recording paper from getting wet by storing the printed recording paper inside a drip-proof cover as the printed paper is fed out in continuous form. For this purpose, the drip-proof cover is mounted so as to cover an area extending from an upper face of a body case 1, where the paper exit port is provided, to a lower face of the body case 1 by passing the rear of a paper holder 13, and the printed recording paper is stored inside the cover. Accordingly, the portable electronic apparatus disclosed in patent document 1 can prevent rain drops from entering the interior through the paper exit port even if the apparatus is exposed to some rain. However, the disadvantage is that the printed recording paper cannot be seen directly unless the drip-proof cover is opened. JP2001-130057 cited in patent document 1 also discloses a portable electronic apparatus having a similar storage cover, in which the position of the axis about which the storage cover is turned to open and close is located closer to the wrist, thereby aiming to improve operability when the storage cover is opened.
Patent document 2 discloses a small portable printer, in which the interior of the printer case is partitioned by a drip-proof wall 12 between a directly underneath area 8 and a drip-proof area 9, the structure being such that any liquid entering the directly underneath area 8 through a paper exit port 6 formed in the front surface of the printer case is prevented from entering the drip-proof area 9 but is drained to the outside through a liquid exit port formed in the bottom of the printer case. The technical idea of the small portable printer disclosed in patent document 2 is to protect important internal parts from the infiltration of rain drops by providing the drip-proof wall 12, while allowing the rain drops infiltrating through the paper exit port to pass through the interior of the printer case and drain to the outside through the bottom, but the structure is not intended to prevent the infiltration of rain drops.
Patent document 3 discloses a printer in which a cover 12 for opening and closing a print paper exit port is related with a printer operation button so that the printer can operate only after the printer is set ready for operation by opening the cover 12. The small portable printer disclosed in patent document 3 thus prevents erroneous print operations.
Patent document 4 discloses a printer in which the sliding operation of a slide cover provided on a main body 13 is related with the operation of a print button so that the print button 18 cannot be operated unless the slide cover is slid into a print position. The small portable printer disclosed in patent document 4 thus prevents erroneous print operations.    Patent document 1: JP2005-288992-A    Patent document 2: JP2005-88350-A    Patent document 3: JP2001-199122-A    Patent document 4: JP2002-23255-A